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Community and Q&A

Stucco drainage wrap over exterior Roxul

pbout | Posted in Green Building Techniques on

Does anyone have installation details for a stucco drainage plane product that can be installed over rigid insulation? An example product is Boral drain n dry, but I can’t find details for a rigid foam install.

The alternate install would be 1×4 vertical furring strips over the Roxul, then paper backed lathe over that for stucco base.

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  1. Expert Member
    Michael Maines | | #1

    Phil, EIFS manufacturers have systems for that. One example is StoPowerwall CI:

  2. pbout | | #2

    Thanks Michael. When I look at the Boral product, their drain wrap replaces the lath, but the StoDrainScreen still requires lath over the top.
    Also, EIFS is lighter than standard stucco, right? Is there something that works with the weight of 3-coat stucco?

  3. Expert Member
    Michael Maines | | #3

    Phil, sorry but I don't have any experience with stucco; I just know that Sto is a well-regarded brand name.

    I have found Boral's customer service to be excellent--have you tried contacting them?

  4. pbout | | #4

    I did speak to Boral. They don't have specific testing on Drain n Dry over exterior insulation; instead, they emphasized that their product is equivalent (or actually stronger) than a traditional metal lath, so you can use it where any metal lath would normally be used.

    They sent the following documents (attached): the Drain-N-Dry product sheet, showing this equivalency to lath; an engineering certification on using Boral stone products over rigid insulation, including fastener info; and the MVMA installation guide, which has fastener guidelines for masonry products installed over exterior foam on wood framing (Table 4).

    There is not a single document that lists this product exactly for the rigid foam application, but you could infer that it works by looking at each of these documents. I think that will be a tough sell for a plan checker.

    I'm also unsure about how a drainage material like this will work over Roxul versus a more rigid foam. Will compression be an issue, or is that another reason to use furring strips to create a drainage plane instead?

  5. JC72 | | #5

    Before you beat yourself up over the drainage wrap I figured I'd let you know that Roxul recommends backer board attached to the furring strips along with strapping supports (Stucco is HEAVY). See the technical guide on the link below.

  6. pbout | | #6

    John, thanks for that link. I'm pretty sure we are going for furring strips instead of the Boral or other similar drain wrap product, so the Roxul guide will be pretty applicable here.

    Do you know if this is an actual recommendation from Roxul on how to install stucco, or is it just their representation on how one might install stucco over furring strips? The backer board is shown on page 19, but on the assembly detail on page 7 it looks to be part of the heavy-weight cladding assembly, which could be stucco or any number of things.

    If I were to include a backer board as part of the stucco install, I'd just have to add the additional backer board weight to my furring strip fastener calc. I understand that the big concern on masonry claddings on top of furring strips is the deflection due to inadequate fastener support, which applies with and without a backer board.

    For fastener sizing, I'm using the attached documents as guides for the calculation. Our plan is to install paper backed lath on top of the furring strips, and to fasten per the results of this calculation. As long as the paper keeps the stucco away from the air gap to maintain the drainage plane, I think this design will work.

  7. JC72 | | #7

    @Phil. I would contact Roxul directly but IMO I would go by the detail on page 19.

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